Manufacturers of mobile devices, such as cellular phones, may obtain components of the mobile devices from various sources, including different manufacturers. For example, an application processor in a cellular phone may be obtained from a first manufacturer, while an imaging device or camera may be obtained from a second manufacturer, and a display may be obtained from a third manufacturer. The application processor, the imaging device, the display controller, or other types of device may be interconnected using a standards-based or proprietary physical interface. In one example, an imaging device may be connected using the Camera Serial Interface (CSI) defined by the Mobile Industry Processor Interface (MIPI) Alliance. In another example, a display may include an interface that conforms to the Display Serial Interface (DSI) standard specified by the Mobile Industry Processor Interface (MIPI) Alliance.
The C-PHY interface, which is a multiphase three-wire interface defined by the MIPI Alliance, uses a trio of conductors to transmit information between devices. Each of the three wires may be in one of three signaling states during transmission of a symbol over the C-PHY interface. Clock information is encoded in a sequence of symbols transmitted on the C-PHY interface and a receiver generates a clock signal from transitions between consecutive symbols. The maximum speed of the C-PHY interface and the ability of a clock and data recovery (CDR) circuit to recover clock information may be limited by the maximum time variation related to transitions of signals transmitted on the different wires of the communication link. A receiver may employ delay circuits to ensure that all of the conductors in the trio have assumed a stable signaling state before providing a sampling edge. The transmission rate of the link may be limited by the delay values used, and there is an ongoing need for optimizing and calibrating clock generation circuits that can function reliably as signaling frequencies of multi-wire interfaces increase.